Fluidized bed for controlled heat treatment



United States inventors Appl. No, Filed Patented Assignee Priority atent Hans Geipel Oberhausen-Sterkrade;

- Eckehard Forster, Oberhausen; Wilfried Heinemann, Duisburg-Hamborn, Germany 710,333

Mar. 4, 1968 Dec. 29, 1970 Huttenwerk Oberhausen A. G. Oberhausen, Rhld., Germany a corporation of Germany Mar. 4, 1967 Germany No. B62030 FLUIDIZED BED FOR CONTROLLED HEAT TREATMENT 6 Claims, 2 Drawing Figs.

266/3 C21d 9/56 Field of Search 266/3, 4, 5,

6. (Recent); 263/3; 148/156; 118/400.5

[56] References Cited UNITED STATES PATENTS 2.795.054 6/ l 957 Bowen 111 263/3X 3.355.159 11/1967 Ayers 266/3 3,391,915 7/1968 Morgan 266/3 3,445,100 5/1969 Bond 266/3 Primary Examiner.l. Spencer Overholser Assistant Examiner-R. Spencer Annear Attorney-Karl F. Ross ABSTRACT: Goods to be heat-treated, e.g. coils of steel wire to be subjected to controlled cooling, are placed on an apertured conveyor passing through a tunnel into which solid ceramic particles entrained by a stream of carrier gas are admitted through a perforated base below the conveyor, the particles enveloping the conveyed goods and being then recirculated through a cooling chamber restoring their original temperature. Further cooling of the particles is effected by two sets of tubes traversing the tunnel below and above the conveyor, respectively.

COOLING Z0 CHAMBE R 8 U a Our present invention relates to a fluidized bed for the heat treatment of workpieces, particularly but not exclusively for the cooling of steel wire which is to be patented (i.e. cooled at a controlled rate) for transformation from itsaustenitic state to a sorbitic pearlite structure asmore fully disclosed in our commonlyowned application Ser. No. 675,522 filed Oct. I6, 1967, now U.S. Pat. No. 3,525,507.

The term fluidized bed" denotes a mass of solid particles, such as ceramic granules, entrained by a current of a preferablyinert carrier gas. The particles, which should have an elevated heat-transfer, coefficient, serve as the principal constituent of the heating or coolingmedium whereas the carrier gas plays only a minor role in the maintenance of the desired discharge temperature. This gasis also used as a vehicle for a continuous recirculation .of the particles through a heat-treating tunnel and. through an external reconditioning chamber where the particles are reheated or recooled to reestablish their original treatmenttemperature.

In another copending application of ours, Ser. No. 704,956 filed Feb. 12, 1968, now U.S. Pat. No. 3,522,936, under the title FLUIDIZED BED FOR HEAT-TREATING PURPOSES, we have disclosed a circulation system for the treatment agent which causes the gas stream to pass upwardly through the tunnel from a perforated base underneath an apertured conveyor, the system including pneumatic control means for concentrating the gas flow in a region of the tunnel spaced from the outlet port and preferably also from the inletport, to simplify the problem of preventing the escape of particles from the-tunnel.

Although the arrangements described in these prior applications are satisfactory for many purposes, difficulties sometimes arisewhen a particularly intensive heat treatment (eg. rapid cooling) is desired. This is true because, as our tests have shown, the thermal conductivity of the fludized bed is relatively limited in a horizontal direction, i.e. in a plane. generally transverse to the direction of particle circulation through the tunnel, with the result that even the supplementalheating or I cooling of the tunnel wall will not significantly alter the rate of heat transfer between the goods and the treatment agent.

It is, therefore, the principal object of our present invention to provide, in a heat-treating system of the general character referred to,.means for more effectively controlling the heat exchange between a fluidized bed and the goods to be treated (cg. cooled) therein.

A more specific object is to provide auxiliary temperature control means for the purpose described which will not materially interfere with the flow of the particles or the movement of the goods through the tunnel.

These objects are realized, pursuant to our present invention, by the provision of at least one set of conduits traversing .the tunnel in the vicinity of the conveyor carrying the goods,

preferably inthe region between this conveyor and the underlying base. Another set of such conduits may be disposed above the conveyor, with enough spacing therefrom to give clearance to the goods to be treated. These conduits serve for the circulation of a temperature-controlling gas or liquid from an external source through the tunnel and, forextended heatexchange contact with the solid particles of the bed, should have an oblong cross section with a major dimension in the direction of particle flow (i.e. I vertical). Thus, each set of conduits may comprise a bank of horizontally juxtaposed pipes of ellipsoidal section traversing the tunnel either transversely or longitudinally, preferably the latter so that fluid may be circulated therethrough in counterflow to the goods. The spacing of the pipessufficient to give passage to the rising particles, need not be uniformand advantageously is reduced in regions of greater accumulation of the goods to be treated. thus near the longitudinal edges of the conveyor in the case of a system for the cooling of coiled wire or the like.

The invention will be described in greater detail with reference to the accompanying drawing in which:

FIG. 1 is a longitudinal sectional view illustrating, somewhat diagrammatically, a system of the type described in our lastmentioned application modified in accordance with ourpresent improvement; and

FIG. 2 is a cross-sectional view taken on the line II-II of FIG. 1.

The system shown in the drawing comprises an apertured conveyor 4, in the form of an endless belt such as a wire netting or a set of parallel wires, mounted on a pair of rollers 14', 14" which are driven by a motor not shown to advance the conveyor in the direction indicated by arrow A, i.e. with its upper run moving from right to left. This upper run traverses an elongated tunnel 3 having an inlet port 5 and an exit port 6 at approximately the same level. A perforated base 15 within tunnel 3, disposed underneath the upper. conveyor run, is spaced from the tunnel bottom to define therewith a manifold for the circulation of a treatment agent of the aforedescribed character, i.e. a stream of gas entraining a mass of solid particles 2 (e.g. of magnesia). Circulation is effected by means of a blower 16 in a conduit 17 which also includes a reconditioning chamber 18, i.e. a cooling chamber if the goods to be treated are coils of steel wire to be patented. These coils, indicated at 1, are deposited on the conveyor 4 at alocation l9 upstream from tunnel 3, advantageously with the aid of a transversely oscillating dispenser as disclosed and claimed in our commonly owned copending application Ser. No. 675,405 filed 16 Oct. 1967. Conduit l7 communicates by way of respective branches 17a, 17b, 17c with sections 9, 10, 11 of the manifold bounded by base l5, these sections being formed by a pair of valves 21 1,2112, 210 so adjusted that the flow rate through manifold sections 9 and 11 is sharply throttled in comparison with the rate of flow through central section 10. Further flow control maybe achieved with the aid of valves 22a, 22b, 220 in branches 20a, 20b, 200, respectively.

With the arrangement illustrated, the bulk of the particles 2 accumulates above manifold section 10 on base"l5 in a pile having a substantially uniform depth d, the pile being sharply stepped at 12 and 13 (i.e. above partitions 7 and 8) down to a height which is well below the level of the goods 1 and which may be equal to approximately 0.3:] while the elevation of the conveyor above base 15 is about0.5d. With the ports 5 and 6 thus located above the pile surface, few if any particles 2 will leave'the tunnel 'by either port. As the distance between steps l2 and 13 is well defined by the separation of partitions 7 and 8 the residence time of thegoods in the pile of particles 2 can be readily predetermined.

In accordance with our present invention, two horizontal banks of heat-conductive (metallic) pipes 31, 32 are disposed below and above the conveyor 4, respectively, the two banks being connected in parallel between an inlet duct 33 and an outletduet 34 for a cooling fluid. As best seen in FIG. 2, these pipes are of ellipsoidal cross section with a vertical major axis a and a horizontal minor axis b whose ratio may be approximately 10:1. The mutual separation of the pipes of each bank, on the order of millimeters, is seen to be greater at the center of the tunnel than near the edges of the conveyor 4, i.e. in the regions where the turns of the cooled wire 1 overlap so as to constitute accumulations of hot metal. It will be noted that the lower pipes. 3l make contact with the broad bottom portion of pile 2 rising from base 15 whereas the upper pipes 32 traverse only the restricted peak of that pile bounded by steps 12 and 13.

As described in our aforementioned copending application Ser. No. 675,522, the operating temperature of chamber 18 and/or the speed of conveyor 4 may be varied in response to measurements of the temperature of the goods at the exit port 6; the fluid circulating through pipes 31 and 32 may be sub jected to the same type of temperature control.

We claim:

ll. A fluidized bed for the heat treatment of workpieces, comprising an elongated tunnel with an inlet port and an outlet port disposed at opposite ends thereof and substantially at the same level;

an apertured conveyor passing through said tunnel by way of said inlet and outlet ports;

a perforated base in said tunnel underneath said conveyor;

circulation means for blowing a treatment agent upwardly through said base into said tunnel and withdrawing said treatment agent from said tunnel for reconditioning, said treatment agent consisting of a gas stream with entrained solid particles;

and auxiliary temperature-control means including a bank of horizontally juxtaposed pipes for the circulation of a heat-exchanging fluid, said pipes passing generally horizontally through said tunnel, said base and said conveyor for contact with said particles, said pipes being of oblong cross section with a major vertical dimension.

2. A fluidized bed as defined in claim 1. further including another bank of juxtaposed pipes for said fluid above said conveyor.

3. A fluidized bed as defined in claim 1, wherein said pipes extend longitudinally of said tunnel.

4. A fluidized bed as defined in claim 3 wherein said pipes are mutually separated with relatively wide spacing near the center of said conveyor and with relatively narrow spacing near the longitudinal edges of said conveyor.

5. A fluidized bed as defined in claim 1 wherein said cross section is generally ellipsoidal with a major vertical axis and a minor horizontal axis, the ratio of said axes being on the order of lOzl.

6. A fluidized bed for the heat treatment of workpieces, comprising an elongated tunnel with an inlet port and an outlet port disposed at opposite ends thereof and substantially at the same level:

an apertured conveyor passing through said tunnel by way of said inlet and outlet ports;

a perforated base in said tunnel underneath said conveyor;

circulation means for blowing a treatment agent upwardly through said base into said tunnel and withdrawing said treatment agent from said tunnel for reconditioning, said treatment agent consisting of a gas stream with entrained solid particles; and

auxiliary temperature-control means including a bank of horizontally juxtaposed pipes for the circulation of a heatexchanging fluid, said pipes passing generally horizontally and longitudinally through said tunnel between said conveyor and said base for contact with said particles, said pipes being mutually separated with relatively wide spacing near the center of said conveyor and with relatively narrow spacing near the longitudinal edges of said conveyor. 

